An edge light-type backlight is widely used as a backlight for a liquid crystal display in a liquid crystal television, a personal computer or the like. In an edge light-type backlight, light from a primary light source (e.g., an LED) disposed on at least one side face side of a light guide plate enters the light guide plate and emits from the whole of one principal plane (light emitting surface) of the light guide plate, and therefore the light can be emitted as planar light.
Such an edge light-type backlight therefore has been applied to lighting equipment which is used by attaching to a ceiling surface or the like of an office, a house or the like (see Patent Literature 1, for example).
Furthermore, an edge light-type lighting device having an LED as a light source has been widespread, since improvement in luminous efficiency and the cost reduction of an LED in recent years have enabled weight saving of lighting equipment by thinning and also have realized light performance fitting user's lifestyle using a dimming function, which is a strong point of an LED, in lighting equipment having an LED as a light source (see Patent Literature 2, for example).
Furthermore, in order to further increase light utilization efficiency by a light guide plate, Patent Literature 3, for example, suggests a light guide plate wherein a number of protruded strip patterns each having a trapezoidal cross section are formed on a light emitting surface of the light guide plate at a predetermined pitch and a number of recessed strip patterns each having a V-shaped (V groove-shaped) cross section are formed on a bottom surface, which is a face opposite to the light emitting surface of the light guide plate, at a predetermined pitch.
According to the invention of Patent Literature 3, light which has entered a light guide plate through a light entering end face is efficiently reflected at an oblique surface of each recessed strip pattern, which is formed on a bottom surface and has a V-shaped (V groove-shaped) cross section, toward light emitting surface, and the reflected light is transmitted through each protruded strip pattern, which is formed on a light emitting surface of the light guide plate and has a trapezoidal cross section, and can emit in the front direction of the light emitting surface as planar light.
It is to be noted that the protruded strip patterns on the light emitting surface of the light guide plate are extended in a direction perpendicular to the light entering end face while the recessed strip patterns on the bottom surface (face opposite to the light emitting surface) of the light guide plate are extended in a direction parallel to the light entering end face.